A négy lépésben, UD, RD, ND és TD utak szerint eltérő sebességű hengerléssel alakított Al 7075 alumínium ötvözet mechanikai és mikroszerkezeti vizsgálata megmutatta, hogy ezzel a technikával ultra-finomszemcsés mikroszerkezet állítható elő. A négy különböző alakítási út jelentősen befolyásolja a kialakuló mikroszerkezetet és az anyag mechanikai viselkedését.
A szilárdsági mérőszámok megközelítőleg azonosnak adódtak mind a négy út esetén, míg a szívóssági mérőszámok az UD és ND utak esetén voltak a legnagyobbak, és TD út esetén a legkisebbek. Az átlagos krisztallitméret és a diszlokációsűrűség az UD és ND utak esetén volt a legnagyobb, a TD út esetén a legkisebb.
8 Új tudományos eredmények
1. Kidolgoztam egy numerikus eljárást, amellyel végeselemes számítások eredményeiből a kombinált Euler-Lagrange leírás alapján előállítható a folytonos sebességmező és a sebesség gradiens mező összenyomhatatlan anyag kétdimenziós, időben állandósult, áramlása esetén. A végeselemes számításokból eredő hibák (zaj) hatásának kiküszöbölésére az áramvonalak előállításánál köbös simító spline illesztést alkalmaztam. [III.].
◊ A hibák hatása a p simító paraméter értékének 0,7 és 0,9 közötti megválasztásával megszüntethető anélkül, hogy az alakváltozás leírása pontatlanná válna.
2. Kidolgoztam egy számítási módszert, amely alkalmas az alakító eljárások nem- monotonitásának számszerű jellemzésére, és kapcsolatba hozható az ultra- finomszemcsés anyag kialakulásával. A bevezetett υ1 mennyiség értéke egységnyi egyenértékű képlékeny alakváltozás esetén a 0-2 intervallumban változik.
[I.][II.][III.][IV].
∫
− ⋅=t dt
d d
0 max
eq.
1 w ω
ν
w- merevtest-szerű forgás szögsebességvektora, ω- alakváltozási sebesség főirányainak forgásvektora
deq.- egyenértékű alakváltozási sebesség, dmax- legnagyobb egyenértékű alakváltozási sebesség
◊ Minél nagyobb υ1 értéke annál jobban eltér az alakváltozási folyamat a monotontól. Különböző mechanikai sémájú, de azonos alakváltozási mértékű folyamatok közül υ1 értéke az egyszerű nyírással megvalósuló deformációk esetén a legnagyobb.
◊ Két képlékenyalakító folyamat közül, amelyiknél a υ1 értéke nagyobb, kisebb alakváltozás hatására várható az ultra-finomszemcsés szerkezet kialakulása.
3. Kimutattam, hogy a szimmetrikus, valamint az UD, RD, ND és TD utak szerinti eltérő sebességű hengerlés a nem-monotonitás szempontjából eltér egymástól. A vizsgált négylépéses alakítás után ez az eltérés a keresztmetszet különböző pontjaiban 25-100%-ot ér el. [II.][III.].
◊ Az eltérő sebességű hengerlésre a szimmetrikushoz képest nagyobb nem-monotonitás jellemző, valamint a υ1 nem-monotonitási mérőszám eloszlása a keresztmetszetben a többlépéses hengerlés után egyenletesebb.
◊ Többlépéses eltérő sebességű hengerlés hatására a υ1 nem-monotonitási mérőszám eloszlása a keresztmetszetben az UD és ND utak esetén aszimmetrikus, míg RD és TD utak esetén szimmetrikus.
4. Kimutattam, hogy a négy lépésben, az UD, ND, RD és TD utak szerint, eltérő sebességű (10 ford./perc −−−− 4 ford./perc) hengerléssel Al 7075 ötvözetben ultrafinom (400-500 nm) szemcseszerkezet állítható elő. Megállapítottam továbbá, hogy a négy különböző alakítási út jelentősen befolyásolja a kialakuló mikroszerkezetet és az anyag mechanikai viselkedését.
◊ A szilárdsági mérőszámok megközelítőleg azonosak mind a négy út esetén, míg a szívóssági mérőszámok az UD és ND utaknál a legnagyobbak, és TD út esetén a legkisebbek.
◊ A diszlokációsűrűség az UD és ND utak esetén a legnagyobb 5,61014 és 5,51014 m-2, a TD út esetén a legkisebb 3,41014 m-2.
9 Publikációk
[I.] Bobor K. Krállics Gy. Characterization of metal-forming processes with respect to non- monotonity, Journal of Physics Conference Series 240, 2010, 012126
[II.] Bobor K. Krállics Gy. Characterization of severe plastic deformation techniques with respect to non-monotonity, Review on Advanced Materials Science 25, 2010, 32-41 [III.] Bobor K. Krállics Gy. Study of non-monotonity of forming processes using finite element
analisys, Materials Science Forum 659, 2010, 373-379
[IV.] Bobor K. Krállics Gy. Könyöksajtolás különböző alakítási útjainak vizsgálata nem- monotonitás szempontjából, OGÉT 2010, XVIII. Nemzetközi Gépészeti Találkozó, konferenciakötet, 71-74
[V.] Bobor Kristóf, Májlinger Kornél, Felületi réteg kialakulása öntöttvas motorblokkok hengerfuratának falán lézerkezelés hatására, OGÉT 2010, XVIII. Nemzetközi Gépészeti Találkozó, konferenciakötet, 283-286
[VI.] Bobor Kristóf, Májlinger Kornél, Szabó Péter János, Formation of Surface Layer on Cast Iron Cylinder Bore due to Nanosecond Laser Impulses, Periodica Polytechnica Mech. Eng. 53, 2009:2, 75-80
10 Short abstract, summary of the theses
SEVERE PLASTIC DEFORMATION WITH ASYMMETRIC ROLLING Kristóf Bobor
PhD theses
Short abstract
The method of severe plastic deformation (SPD) is one of the often used methods to produce bulk ultra-fine grained materials. SPD is a procedure, whereby the structure of the material changes from the initial coarse grained state to ultra-fine grained structure. For these techniques shear deformation as well as the so-called non-monotonic deformation are characteristic. The differential speed rolling is an SPD technique, whereby the material is deformed by two rolls with equal diameter but different speed.
The investigation of the symmetrical and differential speed rolling of Al 7075 aluminium alloy was performed according to different deformation routes. The microstructure and the mechanical properties of the materials produced in different ways were studied.
A quantity and its calculation for the characterization of non-monotonity were introduced, which allows the studying of forming processes in arbitrary coordinate system. The value of this quantity is related to the evolution of ultra-fine grained microstructure. In order to allow the use of this method in case of finite element calculations, I developed a procedure based on the combined Euler-Lagrange description.
Conventional and severe plastic deformation techniques were studied with respect of non-monotonity using this method as well as the non-monotonity analysis of
Theses
1. I introduced a numerical method based on the combined Euler-Lagrange description wherewith the continuous velocity field and the velocity gradient field can be calculated in case of steady state two dimensional flow of incompressible material. By the calculation of the streamlines I applied cubic smoothing spline to eliminate the effect of the errors (noise) from the finite element calculations.
• The effect of the errors can be eliminated with choosing the p smoothing parameter between 0.7 and 0.9 without to become the description of the deformation inaccurate.
2. I introduced a calculation method, which is appropriate to quantitative characterization of the monotonity of forming processes and related to the evolution of ultra-fine grained microstructure. The value of the introduced υ1 quantity is changing in the 0-2 interval in case of unit equivalent plastic deformation.
∫
− ⋅=t dt
d d
0 max
eq.
1 w ω
ν
w- angular velocity vector of rigid body rotation,
ω- rotation vector of the principal axis of rate of deformation tensor deq.- equivalent strain rate, dmax- highest values of equivalent strain rate
• The higher the value of υ1 is, the more the deformation process differs from the monotonic one. From two deformation process with the same amount of deformation, but different mechanical scheme, the value of υ1 is the highest by those of which are realized through simple shear deformation.
• From two forming processes, whereat the value of υ1 is higher the evolution of the ultra-fine grained microstructure can be expected by smaller amount of deformation.
3. I proved that the symmetrical and differential speed rolling according to the routes UD, RD, ND and TD differ from each other in the respect of non-monotonity. After the investigated four-step rolling this difference reaches the 25-100% in different points of the cross section.
◊ Compare to the symmetrical rolling, for the differential speed rolling higher non-monotonity is characteristic, and the value of υ1 is more evenly distributed through the cross section after the multi-step rolling.
◊ After multi-step differential speed rolling, the distribution of the value of υ1 is symmetrical through the cross section in case of UD and ND routes and asymmetrical in case of RD and TD routes.
4. I proved that througth four step differential speed rolling (10 rpm − 4 rpm) according to the UD, ND, RD and TD routes in Al 7075 aluminium alloy an ultra-fine grained (400- 500 nm) microstructure can be produced. Furthermore I determined that the four different deformation routes influence significantly the evolved microstructure and the mechanical behavior of the material.
◊ The strength quantities are approximately equal for all four routes, while the toughness was the highest for UD and ND routes and lowest for TD route.
The dislocation density was the highest for UD and ND routes 5,61014 and 5,51014 m-2, and the lowest for TD route 3,41014 m-2.
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12 Mellékletek
12.1 ábra: A végeselemes számításokhoz felhasznált Al7075 alumínium ötvözet folyásgörbéi különböző
alakváltozási sebesség mellett.
12.1 táblázat: Szűkülő csatornában történő anyagáramlás végeselemes vizsgálatának eredményei. Alakváltozások és
MNM értékek a keresztmetszet különböző pontjaiban, a középponttól t0 távolságra
keresztmetszet ε ν1 ν2
(%) (-) (-) (-)
6,2 0,37 0,44 0,41
18,7 0,34 0,22 0,12
25 0,35 0,20 0,13
31,2 0,35 0,22 0,14
37,5 0,35 0,20 0,15
43,7 0,35 0,20 0,16
46,8 0,33 0,17 0,14
50 0,33 0 0
53,1 0,33 0,17 0,14
56,2 0,35 0,20 0,16
62,5 0,35 0,20 0,15
68,7 0,35 0,22 0,14
75 0,35 0,20 0,13
81,2 0,34 0,22 0,12
93,7 0,37 0,44 0,41
12.2 táblázat: Csavarás és súrlódás nélküli zömítés, alakváltozás és MNM értékek
v0 0 0,25 0,5 0,75 1
ω0 1 0,75 0,5 0,25 0
ε (-) ν1= ν2
0 0 0 0 0 0
0,5 0,42 0,41 0,37 0,29 0
1 0,86 0,79 0,69 0,50 0
1,5 1,3 1,15 0,94 0,66 0
2 1,75 1,47 1,16 0,80 0